Bonded semiconductor devices having processor and static random-access memory and methods for forming the same

ABSTRACT

Embodiments of semiconductor devices and fabrication methods thereof are disclosed. In an example, a semiconductor device includes a first semiconductor structure including a processor and a first bonding layer including a plurality of first bonding contacts. The semiconductor device also includes a second semiconductor structure including an array of static random-access memory (SRAM) cells and a second bonding layer including a plurality of second bonding contacts. The semiconductor device further includes a bonding interface between the first bonding layer and the second bonding layer. The first bonding contacts are in contact with the second bonding contacts at the bonding interface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of International Application No.PCT/CN2019/105313, filed on Sep. 11, 2019, entitled “BONDEDSEMICONDUCTOR DEVICES HAVING PROCESSOR AND STATIC RANDOM-ACCESS MEMORYAND METHODS FOR FORMING THE SAME,” which is incorporated herein byreference in its entirety.

BACKGROUND

Embodiments of the present disclosure relate to semiconductor devicesand fabrication methods thereof.

In modern microprocessors including central processing units (CPUs) andgraphics processing units (GPUs), the cache size is playing anincrementally important role for processor performance enhancement. Acache is a smaller, faster memory, closer to a processor core (e.g., thedistance in the order of millimeters to a few centimeters), which storescopies of the data from frequently-used main memory locations. Mostprocessors have different independent caches, including instruction anddata caches, where the data cache is usually organized as a hierarchy ofmore cache levels (e.g., L1, L2, L3, L4, etc.). A cache is usuallyformed of an array of dense static random-access memory (SRAM) cells.

SUMMARY

Embodiments of semiconductor devices and fabrication methods thereof aredisclosed herein.

In one example, a semiconductor device includes a first semiconductorstructure including a processor and a first bonding layer including aplurality of first bonding contacts. The semiconductor device alsoincludes a second semiconductor structure including an array of SRAMcells and a second bonding layer including a plurality of second bondingcontacts. The semiconductor device further includes a bonding interfacebetween the first bonding layer and the second bonding layer. The firstbonding contacts are in contact with the second bonding contacts at thebonding interface.

In another example, a method for forming a semiconductor device isdisclosed. A plurality of first semiconductor structures are formed on afirst wafer. At least one of the first semiconductor structures includesa processor and a first bonding layer including a plurality of firstbonding contacts. A plurality of second semiconductor structures areformed on a second wafer. At least one of the second semiconductorstructures includes an array of SRAM cells and a second bonding layerincluding a plurality of second bonding contacts. The first wafer andthe second wafer are bonded in a face-to-face manner, such that the atleast one of the first semiconductor structures is bonded to the atleast one of the second semiconductor structures. The first bondingcontacts of the first semiconductor structure are in contact with thesecond bonding contacts of the second semiconductor structure at abonding interface. The bonded first and second wafers are diced into aplurality of dies. At least one of the dies includes the bonded firstand second semiconductor structures.

In still another example, a method for forming a semiconductor device isdisclosed. A plurality of first semiconductor structures are formed on afirst wafer. At least one of the first semiconductor structures includesa processor and a first bonding layer including a plurality of firstbonding contacts. The first wafer is diced into a plurality of firstdies, such that at least one of the first dies includes the at least oneof the first semiconductor structures. A plurality of secondsemiconductor structures are formed on a second wafer. At least one ofthe second semiconductor structures includes an array of SRAM cells anda second bonding layer including a plurality of second bonding contacts.The second wafer is diced into a plurality of second dies, such that atleast one of the second dies includes the at least one of the secondsemiconductor structures. The first die and the second die are bonded ina face-to-face manner, such that the first semiconductor structure isbonded to the second semiconductor structure. The first bonding contactsof the first semiconductor structure are in contact with the secondbonding contacts of the second semiconductor structure at a bondinginterface.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present disclosure,and together with the description, further serve to explain theprinciples of the present disclosure and to enable a person skilled inthe pertinent art to make and use the present disclosure.

FIG. 1A illustrates a schematic view of a cross-section of an exemplarysemiconductor device, according to some embodiments.

FIG. 1B illustrates a schematic view of a cross-section of anotherexemplary semiconductor device, according to some embodiments.

FIG. 2A illustrates a schematic plan view of an exemplary semiconductorstructure having a processor, peripheral circuits, and interfacecircuits, according to some embodiments.

FIG. 2B illustrates a schematic plan view of an exemplary semiconductorstructure having SRAM, according to some embodiments.

FIG. 3A illustrates a schematic plan view of an exemplary semiconductorstructure having a processor and interface circuits, according to someembodiments.

FIG. 3B illustrates a schematic plan view of an exemplary semiconductorstructure having SRAM and peripheral circuits, according to someembodiments.

FIG. 4 illustrates a cross-section of an exemplary semiconductor device,according to some embodiments.

FIG. 5 illustrates a cross-section of another exemplary semiconductordevice, according to some embodiments.

FIGS. 6A and 6B illustrate a fabrication process for forming anexemplary semiconductor structure having a processor and other logiccircuits, according to some embodiments.

FIGS. 7A and 7B illustrate a fabrication process for forming anexemplary semiconductor structure having SRAM, according to someembodiments.

FIGS. 8A and 8B illustrate a fabrication process for forming anexemplary semiconductor device, according to some embodiments.

FIGS. 9A-9C illustrate a fabrication process for bonding and dicing anexemplary semiconductor structure, according to some embodiments.

FIGS. 10A-10C illustrate a fabrication process for dicing and bonding anexemplary semiconductor structure, according to some embodiments.

FIG. 11 is a flowchart of an exemplary method for forming asemiconductor device, according to some embodiments.

FIG. 12 is a flowchart of another exemplary method for forming asemiconductor device, according to some embodiments.

Embodiments of the present disclosure will be described with referenceto the accompanying drawings.

DETAILED DESCRIPTION

Although specific configurations and arrangements are discussed, itshould be understood that this is done for illustrative purposes only. Aperson skilled in the pertinent art will recognize that otherconfigurations and arrangements can be used without departing from thespirit and scope of the present disclosure. It will be apparent to aperson skilled in the pertinent art that the present disclosure can alsobe employed in a variety of other applications.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “some embodiments,” etc.,indicate that the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiments. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of aperson skilled in the pertinent art to affect such features, structuresand/or characteristics in connection with other embodiments whether ornot explicitly described.

In general, terminology may be understood at least in part from usage incontext. For example, the term “one or more” as used herein, dependingat least in part upon context, may be used to describe any feature,structure, or characteristic in a singular sense or may be used todescribe combinations of features, structures or characteristics in aplural sense. Similarly, terms, such as “a,” “an,” or “the,” again, maybe understood to convey a singular usage or to convey a plural usage,depending at least in part upon context. In addition, the term “basedon” may be understood as not necessarily intended to convey an exclusiveset of factors and may, instead, allow for existence of additionalfactors not necessarily expressly described, again, depending at leastin part on context.

It should be readily understood that the meaning of “on,” “above,” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoincludes the meaning of “on” something with an intermediate feature or alayer therebetween, and that “above” or “over” not only means themeaning of “above” or “over” something but can also include the meaningit is “above” or “over” something with no intermediate feature or layertherebetween (i.e., directly on something).

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the term “substrate” refers to a material onto whichsubsequent material layers are added. The substrate itself can bepatterned. Materials added on top of the substrate can be patterned orcan remain unpatterned. Furthermore, the substrate can include a widearray of semiconductor materials, such as silicon, germanium, galliumarsenide, indium phosphide, etc. Alternatively, the substrate can bemade from an electrically non-conductive material, such as a glass, aplastic, or a sapphire wafer.

As used herein, the term “layer” refers to a material portion includinga region with a thickness. A layer can extend over the entirety of anunderlying or overlying structure or may have an extent less than theextent of an underlying or overlying structure. Further, a layer can bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer can be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer can extend horizontally, vertically, and/or along atapered surface. A substrate can be a layer, can include one or morelayers therein, and/or can have one or more layer thereupon, thereabove,and/or therebelow. A layer can include multiple layers. For example, aninterconnect layer can include one or more conductor and contact layers(in which interconnect lines and/or via contacts are formed) and one ormore dielectric layers.

As used herein, the term “about” indicates the value of a given quantitythat can vary based on a particular technology node associated with thesubject semiconductor device. Based on the particular technology node,the term “about” can indicate a value of a given quantity that varieswithin, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% ofthe value).

As used herein, a “wafer” is a piece of a semiconductor material forsemiconductor devices to build in and/or on it and that can undergovarious fabrication processes before being separated into dies.

As modern processor (also known as “microprocessor”) developed into moreadvanced generations, the cache size is playing an incrementallyimportant role for processor performance enhancement. In some cases,cache, which is usually formed of sense high-speed SRAM cells, canoccupy half or even more chip real estate in microprocessor chip. Also,the resistive-capacitive (RC) delay from the cache to the processor corecould become significant to degrade performance. Thus, both interconnectRC delay and the SRAM yield dominate microprocessor performance andyield. However, because the chip size of microprocessor is gettingbigger and bigger in the order of a few centimeters, the RC delay fromSRAM cache to the processor core become significant to degradeperformance.

Various embodiments in accordance with the present disclosure provide asemiconductor device with a processor and SRAM cache integrated on abonded chip to achieve better cache performance (faster data transferwith higher efficiency), wider data bandwidth, and faster memoryinterface speed. The semiconductor device disclosed herein can include afirst semiconductor structure having a processor (e.g., having multipleprocessor cores) and a second semiconductor structure having SRAM (e.g.,as cache) bonded to the first semiconductor structure with a largenumber of short-distance vertical metal interconnects instead of theperipherally-distributed, long-distance metal routing, or evenconventional through silicon vias (TSVs). With the SRAM being directlyabove or below the processor cores, interconnect distance between theprocessor cores and SRAM is shortened, e.g., from the centimeter-levelto micrometer-level, thereby significantly reducing RC delay andchip/circuit board size, as well as increasing data transfer speed.Moreover, shorter manufacturing cycle time with higher yield can beachieved due to less interactive influences from manufacturing processesof the processor wafer and the SRAM wafer as well as the known goodhybrid bonding yield.

FIG. 1A illustrates a schematic view of a cross-section of an exemplarysemiconductor device 100, according to some embodiments. Semiconductordevice 100 represents an example of a bonded chip. The components ofsemiconductor device 100 (e.g., processors and SRAM) can be formedseparately on different substrates and then jointed to form a bondedchip. Semiconductor device 100 can include a first semiconductorstructure 102 including a processor. In some embodiments, the processorin first semiconductor structure 102 uses complementarymetal-oxide-semiconductor (CMOS) technology. The processor can beimplemented with advanced logic processes (e.g., technology nodes of 90nm, 65 nm, 45 nm, 32 nm, 28 nm, 20 nm, 16 nm, 14 nm, 10 nm, 7 nm, 5 nm,3 nm, etc.) to achieve high speed.

The processor can be a specialized processor including, but not limitedto, CPU, GPU, digital signal processor (DSP), tensor processing unit(TPU), vision processing unit (VPU), neural processing unit (NPU),synergistic processing unit (SPU), physics processing unit (PPU), andimage signal processor (ISP). The processor can also be a system-on-chip(SoC) that combines multiple specialized processors, such as anapplication processor, baseband processor, and so on. In someembodiments in which semiconductor device 100 is used in mobile devices(e.g., smartphones, tablets, eyeglasses, wrist watches, virtualreality/augmented reality headsets, laptop computers, etc.), anapplication processor handles applications running in an operatingsystem environment, and a baseband processor handles the cellularcommunications, such as the second-generation (2G), the third-generation(3G), the fourth-generation (4G), the fifth-generation (5G), thesixth-generation (6G) cellular communications, and so on.

A processor can include one or more processing units (also known as“processor cores” or “cores”), each of which reads and executesinstructions, and one or more caches formed of high-speed memory, suchas SRAM. In some embodiments, the processor in first semiconductorstructure 102 does not include an SRAM cell. In other words, a cache isnot included in the processor in first semiconductor structure 102,according to some embodiments. For example, the processor in firstsemiconductor structure 102 may consist of (i.e., include only) one ormore processor cores.

Other processing units (also known as “logic circuits”) besides theprocessor can be formed in first semiconductor structure 102 as well,such as one or more controllers, one or more interface circuits, and theentirety or part of the peripheral circuits of the SRAM in a secondsemiconductor structure 104. A controller can handle a specificoperation in an embedded system. In some embodiments in whichsemiconductor device 100 is used in mobile devices, each controller canhandle a specific operation of the mobile device, for example,communications other than cellular communication (e.g., Bluetoothcommunication, Wi-Fi communication, FM radio, etc.), power management,display drive, positioning and navigation, touch screen, camera, etc.First semiconductor structure 102 of semiconductor device 100 thus canfurther include a Bluetooth controller, a Wi-Fi controller, a FM radiocontroller, a power controller, a display controller, a GPS controller,a touch screen controller, a camera controller, to name a few, each ofwhich is configured to control operations of the corresponding componentin a mobile device.

In some embodiments, first semiconductor structure 102 of semiconductordevice also includes one or more interface circuits configured totransmit and receive a variety type of signals, such as data signals,control signals, state/status signals, command signals, etc., to andfrom semiconductor device 100. The interface circuits can include one ormore bus circuits (e.g., bus interface units) and one or moreinput/output (I/O) circuits. In some embodiments, first semiconductorstructure 102 of semiconductor device 100 further includes the entiretyor part the peripheral circuits of the SRAM of second semiconductorstructure 104. The peripheral circuits (also known as control andsensing circuits) can include any suitable digital, analog, and/ormixed-signal circuits used for facilitating the operations of the SRAM.For example, the peripheral circuits can include one or more of an I/Obuffer, a decoder (e.g., a row decoder and a column decoder), a senseamplifier, or any active or passive components of the circuit (e.g.,transistors, diodes, resistors, or capacitors).

Semiconductor device 100 can also include second semiconductor structure104 including an array of SRAM cells. That is, second semiconductorstructure 104 can be an SRAM memory device. The SRAM and the logiccircuits (e.g., the processor and peripheral circuits) are formed ondifferent substrates and then integrated vertically in semiconductordevice 100, allowing shorter interconnects, less RC delay, and higherdata transfer speed. The memory controller of the SRAM can be embeddedas part of the peripheral circuits in first semiconductor structure 102and/or second semiconductor structure 104. In some embodiments, eachSRAM cell includes a plurality of transistors for storing a bit of dataas a positive or negative electrical charge as well as one or moretransistors that control access to it. In one example, each SRAM cellhas six transistors (e.g., metal-oxide-semiconductor field-effecttransistors (MOSFETs)), for example, four transistors for storing a bitof data and two transistors for controlling access to the data. The SRAMcan enable high-speed operations of semiconductor device 100, used asone or more caches (e.g., instruction cache or data cache) and/or databuffers.

As shown in FIG. 1A, semiconductor device 100 further includes a bondinginterface 106 vertically between first semiconductor structure 102 andsecond semiconductor structure 104. As described below in detail, firstand second semiconductor structures 102 and 104 can be fabricatedseparately (and in parallel in some embodiments) such that the thermalbudget of fabricating one of first and second semiconductor structures102 and 104 does not limit the processes of fabricating another one offirst and second semiconductor structures 102 and 104. Moreover, a largenumber of interconnects (e.g., bonding contacts) can be formed throughbonding interface 106 to make direct, short-distance (e.g.,micron-level) electrical connections between first semiconductorstructure 102 and second semiconductor structure 104, as opposed to thelong-distance (e.g., millimeter or centimeter-level) chip-to-chip databus on the circuit board, such as printed circuit board (PCB), therebyeliminating chip interface delay and achieving high-speed I/O throughputwith reduced power consumption. Data transfer between the SRAM in secondsemiconductor structure 104 and the processor in first semiconductorstructure 102 can be performed through the interconnects (e.g., bondingcontacts) across bonding interface 106. By vertically integrating firstand second semiconductor structures 102 and 104, the chip size can bereduced, and the memory cell density can be increased.

It is understood that the relative positions of stacked first and secondsemiconductor structures 102 and 104 are not limited. FIG. 1Billustrates a schematic view of a cross-section of another exemplarysemiconductor device 101, according to some embodiments. Different fromsemiconductor device 100 in FIG. 1A in which second semiconductorstructure 104 including the array of SRAM cells is above firstsemiconductor structure 102 including the processor, in semiconductordevice 101 in FIG. 1B, first semiconductor structure 102 including theprocessor is above second semiconductor structure 104 including thearray of SRAM cells. Nevertheless, bonding interface 106 is formedvertically between first and second semiconductor structures 102 and 104in semiconductor device 101, and first and second semiconductorstructures 102 and 104 are jointed vertically through bonding (e.g.,hybrid bonding), according to some embodiments. Data transfer betweenthe SRAM in second semiconductor structure 104 and the processor infirst semiconductor structure 102 can be performed through theinterconnects (e.g., bonding contacts) across bonding interface 106.

In some embodiments, first semiconductor structure 102 does not includea SRAM cell, and second semiconductor structure 104 does not include aprocessor. That is, first semiconductor structure 102 can be a dedicatedlogic structure without any memory device (e.g., SRAM), and secondsemiconductor structure can be a dedicated memory structure without anylogic device (e.g., processor core).

FIG. 2A illustrates a schematic plan view of an exemplary semiconductorstructure 200 having a processor, peripheral circuits, and interfacecircuits, according to some embodiments. Semiconductor structure 200 maybe one example of first semiconductor structure 102. Semiconductorstructure 200 can include a processor having a plurality of processorcores 202 on the same substrate as other logic circuits and fabricatedusing the same logic process as other logic circuits. Each processorcore 202 can be a CPU core, a GPU core, a DSP core, an applicationprocessor core, a baseband processor core, to name a few. Other logiccircuits can include interface circuits, such as I/O circuits 204 andbus circuits 206. Other logic circuits can also include all theperipheral circuits for controlling and sensing SRAM 212, including, forexample, row decoders 208, column decoders 210, and any other suitabledevices. FIG. 2A shows an exemplary layout in which processor cores 202,the interface circuits (e.g., bus circuits 206 and I/O circuits 204),and the peripheral circuits (e.g., row decoders 208 and column decoders210) are formed in different regions on the same plane. For example, theinterface circuits (e.g., bus circuits 206 and I/O circuits 204) and theperipheral circuits (e.g., row decoders 208 and column decoders 210) maybe formed outside of processor cores 202.

FIG. 2B illustrates a schematic plan view of an exemplary semiconductorstructure 201 having SRAM 212, according to some embodiments.Semiconductor structure 201 may be one example of second semiconductorstructure 104. By moving all the peripheral circuits (e.g., row decoders208 and column decoders 210) away from semiconductor structure 201(e.g., to semiconductor structure 200), the size of SRAM 212 (e.g., thenumber of SRAM cells) in semiconductor structure 201 can be increased

It is understood that the layouts of semiconductor structures 200 and201 are not limited to the exemplary layouts in FIGS. 2A and 2B. In someembodiments, at least some of processor cores 202, the interfacecircuits (e.g., bus circuits 206 and I/O circuits 204), and theperipheral circuits (e.g., row decoders 208 and column decoders 210) arestacked one over another, i.e., in different planes. For example, theinterface circuits (e.g., bus circuits 206 and I/O circuits 204) and theperipheral circuits (e.g., row decoders 208 and column decoders 210) maybe formed above or below processor cores 202 to further reduce the chipsize.

It is further understood that part or the entirety of the peripheralcircuits of SRAM 212 (e.g., row decoders 208, column decoders 210, andany other suitable devices) may be formed in the same semiconductorstructure in which SRAM 212 is formed. The peripheral circuits of SRAM212 may be distributed in both semiconductor structures 200 and 201,according to some other embodiments. In some embodiments, the peripheralcircuits of SRAM 212 may be formed only in the same semiconductorstructure in which SRAM 212 is formed. For example, FIG. 3A illustratesa schematic plan view of an exemplary semiconductor structure 300 havinga processor and interface circuits, according to some embodiments; FIG.3B illustrates a schematic plan view of an exemplary semiconductorstructure 301 having SRAM and peripheral circuits, according to someembodiments. Different from semiconductor structures 200 and 201 inFIGS. 2A and 2B, semiconductor structure 300 includes processor cores202 and the interface circuits (e.g., bus circuits 206 and I/O circuits204) but does not include any peripheral circuits of SRAM 212. Instead,semiconductor structure 301 includes both SRAM 212 and all theperipheral circuits of SRAM 212 (e.g., row decoders 208, column decoders210, and any other suitable devices). As shown in FIG. 3B, in someembodiments, SRAM 212 is distributed in a plurality of separate regionsin semiconductor structure 301. That is, the cache module formed by SRAM212 can be divided into smaller cache regions, distributing insemiconductor structure 301. In one example, the distribution of thecache regions may be based on the design of the bonding contacts and/orthe peripheral circuits of SRAM 212, e.g., occupying the areas withoutthe bonding contacts and/or the peripheral circuits. In another example,the distribution of the cache regions may be random. As a result, awider design window for SRAM 212 can be arranged achieved.

FIG. 4 illustrates a cross-section of an exemplary semiconductor device400, according to some embodiments. As one example of semiconductordevice 100 described above with respect to FIG. 1A, semiconductor device400 is a bonded chip including a first semiconductor structure 402 and asecond semiconductor structure 404 stacked over first semiconductorstructure 402. First and second semiconductor structures 402 and 404 arejointed at a bonding interface 406 therebetween, according to someembodiments. As shown in FIG. 4, first semiconductor structure 402 caninclude a substrate 408, which can include silicon (e.g., singlecrystalline silicon, c-Si), silicon germanium (SiGe), gallium arsenide(GaAs), germanium (Ge), silicon on insulator (SOD, or any other suitablematerials.

First semiconductor structure 402 of semiconductor device 400 caninclude a device layer 410 above substrate 408. It is noted that x- andy-axes are added in FIG. 4 to further illustrate the spatialrelationship of the components in semiconductor device 400. Substrate408 includes two lateral surfaces (e.g., a top surface and a bottomsurface) extending laterally in the x-direction (the lateral directionor width direction). As used herein, whether one component (e.g., alayer or a device) is “on,” “above,” or “below” another component (e.g.,a layer or a device) of a semiconductor device (e.g., semiconductordevice 400) is determined relative to the substrate of the semiconductordevice (e.g., substrate 408) in the y-direction (the vertical directionor thickness direction) when the substrate is positioned in the lowestplane of the semiconductor device in the y-direction. The same notionfor describing the spatial relationship is applied throughout thepresent disclosure.

In some embodiments, device layer 410 includes a processor 412 onsubstrate 408 and other logic circuits 414 on substrate 408 and outsideof processor 412. In some embodiments, other logic circuits 414 includeinterface circuits for transmitting and receiving signals to and fromsemiconductor device 400 as described above in detail. In someembodiments, other logic circuits 414 include part or the entirety ofthe peripheral circuits for controlling and sensing the SRAM ofsemiconductor device 400 as described above in detail. In someembodiments, processor 412 includes a plurality of transistors 418forming any suitable specialized processor cores and/or SoC cores asdescribed above in detail. In some embodiments, transistors 418 furtherform other logic circuits 414, for example, any suitable I/O circuits orbus circuits for transmitting and receiving signals to and fromsemiconductor device 400, and/or any suitable digital, analog, and/ormixed-signal control and sensing circuits used for facilitating theoperation of the SRAM including, but not limited to, an input/outputbuffer, a decoder (e.g., a row decoder and a column decoder), and asense amplifier.

Transistors 418 can be formed “on” substrate 408, in which the entiretyor part of transistors 418 are formed in substrate 408 (e.g., below thetop surface of substrate 408) and/or directly on substrate 408.Isolation regions (e.g., shallow trench isolations (STIs)) and dopedregions (e.g., source regions and drain regions of transistors 418) canbe formed in substrate 408 as well. Transistors 418 are high-speed withadvanced logic processes (e.g., technology nodes of 90 nm, 65 nm, 45 nm,32 nm, 28 nm, 20 nm, 16 nm, 14 nm, 10 nm, 7 nm, 5 nm, 3 nm, etc.),according to some embodiments.

In some embodiments, first semiconductor structure 402 of semiconductordevice 400 further includes an interconnect layer 420 above device layer410 to transfer electrical signals to and from processor 412 (and otherlogic circuits 414 if any). Interconnect layer 420 can include aplurality of interconnects (also referred to herein as “contacts”),including lateral interconnect lines and vertical interconnect access(via) contacts. As used herein, the term “interconnects” can broadlyinclude any suitable types of interconnects, such as middle-end-of-line(MEOL) interconnects and back-end-of-line (BEOL) interconnects.Interconnect layer 420 can further include one or more interlayerdielectric (ILD) layers (also known as “intermetal dielectric (IMD)layers”) in which the interconnect lines and via contacts can form. Thatis, interconnect layer 420 can include interconnect lines and viacontacts in multiple ILD layers. The interconnect lines and via contactsin interconnect layer 420 can include conductive materials including,but not limited to, tungsten (W), cobalt (Co), copper (Cu), aluminum(Al), silicides, or any combination thereof. The ILD layers ininterconnect layer 420 can include dielectric materials including, butnot limited to, silicon oxide, silicon nitride, silicon oxynitride, lowdielectric constant (low-k) dielectrics, or any combination thereof. Insome embodiments, the devices in device layer 410 are electricallyconnected to one another through the interconnects in interconnect layer420. For example, other logic circuits 414 may be electrically connectedto processor 412 through interconnect layer 420.

As shown in FIG. 4, first semiconductor structure 402 of semiconductordevice 400 can further include a bonding layer 422 at bonding interface406 and above interconnect layer 420 and device layer 410 (includingprocessor 412). Bonding layer 422 can include a plurality of bondingcontacts 424 and dielectrics electrically isolating bonding contacts424. Bonding contacts 424 can include conductive materials including,but not limited to, W, Co, Cu, Al, silicides, or any combinationthereof. The remaining area of bonding layer 422 can be formed withdielectrics including, but not limited to, silicon oxide, siliconnitride, silicon oxynitride, low-k dielectrics, or any combinationthereof. Bonding contacts 424 and surrounding dielectrics in bondinglayer 422 can be used for hybrid bonding.

Similarly, as shown in FIG. 4, second semiconductor structure 404 ofsemiconductor device 400 can also include a bonding layer 426 at bondinginterface 406 and above bonding layer 422 of first semiconductorstructure 402. Bonding layer 426 can include a plurality of bondingcontacts 428 and dielectrics electrically isolating bonding contacts428. Bonding contacts 428 can include conductive materials including,but not limited to, W, Co, Cu, Al, silicides, or any combinationthereof. The remaining area of bonding layer 426 can be formed withdielectrics including, but not limited to, silicon oxide, siliconnitride, silicon oxynitride, low-k dielectrics, or any combinationthereof. Bonding contacts 428 and surrounding dielectrics in bondinglayer 426 can be used for hybrid bonding. Bonding contacts 428 are incontact with bonding contacts 424 at bonding interface 406, according tosome embodiments.

As described above, second semiconductor structure 404 can be bonded ontop of first semiconductor structure 402 in a face-to-face manner atbonding interface 406. In some embodiments, bonding interface 406 isdisposed between bonding layers 422 and 426 as a result of hybridbonding (also known as “metal/dielectric hybrid bonding”), which is adirect bonding technology (e.g., forming bonding between surfaceswithout using intermediate layers, such as solder or adhesives) and canobtain metal-metal bonding and dielectric-dielectric bondingsimultaneously. In some embodiments, bonding interface 406 is the placeat which bonding layers 422 and 426 are met and bonded. In practice,bonding interface 406 can be a layer with a certain thickness thatincludes the top surface of bonding layer 422 of first semiconductorstructure 402 and the bottom surface of bonding layer 426 of secondsemiconductor structure 404.

In some embodiments, second semiconductor structure 404 of semiconductordevice 400 further includes an interconnect layer 430 above bondinglayer 426 to transfer electrical signals. Interconnect layer 430 caninclude a plurality of interconnects, such as MEOL interconnects andBEOL interconnects. In some embodiments, interconnects in interconnectlayer 430 also include local interconnects, such as bit line contactsand word line contacts. Interconnect layer 430 can further include oneor more ILD layers in which the interconnect lines and via contacts canform. The interconnect lines and via contacts in interconnect layer 430can include conductive materials including, but not limited to, W, Co,Cu, Al, silicides, or any combination thereof. The ILD layers ininterconnect layer 430 can include dielectric materials including, butnot limited to, silicon oxide, silicon nitride, silicon oxynitride,low-k dielectrics, or any combination thereof.

Second semiconductor structure 404 of semiconductor device 400 canfurther include an array of SRAM cells 432 above interconnect layer 430and bonding layer 426. Array of SRAM cells 432 can be used as, forexample, cache and/or data buffer of semiconductor device 400. Forexample, array of SRAM cells 432 may function as the internalinstruction cache and/or data cache of processor 412. In someembodiments, each SRAM cell 432 includes a plurality of transistors 434.In some embodiments, SRAM cell 432 is a 6T cell that consists of fourtransistors 434 for storing one bit of data and two transistors 434 forcontrolling access to the data. It is understood that SRAM cell 432 maybe of any suitable configuration, such as more or fewer than sixtransistors (e.g., more or fewer transistors per bit). In someembodiments, transistors 434 are formed “on” a semiconductor layer 440,in which the entirety or part of transistors 434 are formed insemiconductor layer 440 and/or directly on semiconductor layer 440.Isolation regions (e.g., shallow trench isolations (STIs)) and dopedregions (e.g., source regions and drain regions of transistors 434) canbe formed in semiconductor layer 440 as well. In some embodiments, twoaccess transistors 434 (e.g., transistors 434 that control access ofdata) are controlled by a word line, and four storage transistors 434(e.g., transistors 434 that store the bit of data) are coupled to bitlines and controlled by two access transistors 434.

In some embodiments, second semiconductor structure 404 further includessemiconductor layer 440 disposed above and in contact with array of SRAMcells 432. Semiconductor layer 440 can be a thinned substrate on whichtransistors 434 are formed. In some embodiments, semiconductor layer 440includes single-crystal silicon. In some embodiments, semiconductorlayer 440 can include polysilicon, amorphous silicon, SiGe, GaAs, Ge, orany other suitable materials. Semiconductor layer 440 can also includeisolation regions and doped regions (e.g., as the sources and drains oftransistors 434).

As shown in FIG. 4, second semiconductor structure 404 of semiconductordevice 400 can further include a pad-out interconnect layer 444 abovesemiconductor layer 440. Pad-out interconnect layer 444 can includeinterconnects, e.g., contact pads 446, in one or more ILD layers.Pad-out interconnect layer 444 and interconnect layer 430 can be formedat opposite sides of semiconductor layer 440. In some embodiments,interconnects in pad-out interconnect layer 444 can transfer electricalsignals between semiconductor device 400 and outside circuits, e.g., forpad-out purposes. In some embodiments, second semiconductor structure404 further includes one or more contacts 448 extending throughsemiconductor layer 440 to electrically connect pad-out interconnectlayer 444 and interconnect layers 430 and 420. As a result, processor412 and array of SRAM cells 432 (and other logic circuits 414 if any)can be electrically connected to outside circuits through contacts 448and pad-out interconnect layer 444.

Moreover, processor 412 (and other logic circuits 414 if any) can beelectrically connected to array of SRAM cells 432 through interconnectlayers 430 and 420 as well as bonding contacts 428 and 424. Byvertically integrating processor 412 and array of SRAM cells 432, theinterconnect distance can be significantly reduced compared withlaterally arranging processor 412 and array of SRAM cells 432 in thesame plane of a microprocessor chip, which has a chip size in thecentimeter-level. The vertical distance between processor 412 and arrayof SRAM cells 432 is less than 1 mm, according to some embodiments. Inone example, the vertical distance between processor 412 and array ofSRAM cells 432 is between 1 μm and 1 mm (e.g., 1 μm, 2 μm, 3 μm, 4 μm, 5μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70μm, 80 μm, 90 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400μm, 450 μm, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850μm, 900 μm, 950 μm, 1 mm, any range bounded by the lower end by any ofthese values, or in any range defined by any two of these values).

FIG. 5 illustrates a cross-section of another exemplary semiconductordevice 500, according to some embodiments. As one example ofsemiconductor device 101 described above with respect to FIG. 1B,semiconductor device 500 is a bonded chip including a secondsemiconductor structure 504 and a first semiconductor structure 502stacked over second semiconductor structure 504. Similar tosemiconductor device 400 described above in FIG. 4, semiconductor device500 represents an example of a bonded chip in which first semiconductorstructure 502 including a processor and second semiconductor structure504 including SRAM are formed separately and bonded in a face-to-facemanner at a bonding interface 506. Different from semiconductor device400 described above in FIG. 4 in which first semiconductor structure 402including the processor is below second semiconductor structure 404including the SRAM, semiconductor device 500 in FIG. 5 includes firstsemiconductor structure 502 including the processor disposed abovesecond semiconductor structure 504 including the SRAM. It is understoodthat the details of similar structures (e.g., materials, fabricationprocesses, functions, etc.) in both semiconductor devices 400 and 500may not be repeated below.

Second semiconductor structure 504 of semiconductor device 500 caninclude a substrate 508 and an array of SRAM cells 510 on substrate 508.In some embodiments, each SRAM cell 510 includes a plurality oftransistors 512. SRAM cell 510 can be a 6T cell consisting of fourstorage transistor and two access transistors. It is understood thatSRAM cell 510 may be of any suitable configuration, such as more orfewer than six transistors (e.g., more or fewer transistors per bit). Insome embodiments, transistors 512 are formed “on” substrate 508, inwhich the entirety or part of transistors 512 are formed in substrate508 and/or directly on substrate 508. It is understood that thestructure and configuration of SRAM cell 510 are not limited to theexample in FIG. 5 and may include any suitable structure andconfiguration.

In some embodiments, second semiconductor structure 504 of semiconductordevice 500 also includes an interconnect layer 514 above array of SRAMcells 510 to transfer electrical signals to and from array of SRAM cells510. Interconnect layer 514 can include a plurality of interconnects,including interconnect lines and via contacts. In some embodiments,interconnects in interconnect layer 514 also include localinterconnects, such as bit line contacts and word line contacts. In someembodiments, second semiconductor structure 504 of semiconductor device500 further includes a bonding layer 516 at bonding interface 506 andabove interconnect layer 514 and array of SRAM cells 510. Bonding layer516 can include a plurality of bonding contacts 518 and dielectricssurrounding and electrically isolating bonding contacts 518.

As shown in FIG. 5, first semiconductor structure 502 of semiconductordevice 500 includes another bonding layer 532 at bonding interface 506and above bonding layer 516. Bonding layer 532 can include a pluralityof bonding contacts 534 and dielectrics surrounding and electricallyisolating bonding contacts 534. Bonding contacts 534 are in contact withbonding contacts 518 at bonding interface 506, according to someembodiments. In some embodiments, first semiconductor structure 502 ofsemiconductor device 500 also includes an interconnect layer 536 abovebonding layer 532 to transfer electrical signals. Interconnect layer 536can include a plurality of interconnects, including interconnect linesand via contacts.

First semiconductor structure 502 of semiconductor device 500 canfurther include a device layer 538 above interconnect layer 536 andbonding layer 532. In some embodiments, device layer 538 includes aprocessor 540 above interconnect layer 536 and bonding layer 532. Insome embodiments, device layer 538 further includes other logic circuits542 above interconnect layer 536 and bonding layer 532 and outside ofprocessor 540. For example, other logic circuits 542 may includeinterface circuits and/or part or the entirety of the peripheralcircuits for controlling and sensing array of SRAM cells 510. In someembodiments, the devices in device layer 538 are electrically connectedto one another through the interconnects in interconnect layer 536. Forexample, other logic circuits 542 may be electrically connected toprocessor 540 through interconnect layer 536.

In some embodiments, processor 540 includes a plurality of transistors544 forming any suitable specialized processor cores and/or SoC cores.Transistors 544 can be formed “on” a semiconductor layer 546, in whichthe entirety or part of transistors 544 are formed in semiconductorlayer 546 and/or directly on semiconductor layer 546. Isolation regions(e.g., STIs) and doped regions (e.g., source regions and drain regionsof transistors 544) can be formed in semiconductor layer 546 as well.Transistors 544 can form other logic circuits 542 as well. Transistors544 are high-speed with advanced logic processes (e.g., technology nodesof 90 nm, 65 nm, 45 nm, 32 nm, 28 nm, 20 nm, 16 nm, 14 nm, 10 nm, 7 nm,5 nm, 3 nm, etc.), according to some embodiments.

In some embodiments, first semiconductor structure 502 further includessemiconductor layer 546 disposed above device layer 538. Semiconductorlayer 546 can be above and in contact with processor 540 and other logiccircuits 542. Semiconductor layer 546 can be a thinned substrate onwhich transistors 544 are formed. In some embodiments, semiconductorlayer 546 includes single-crystal silicon. In some embodiments,semiconductor layer 546 can include polysilicon, amorphous silicon,SiGe, GaAs, Ge, Salicide, or any other suitable materials. Semiconductorlayer 546 can also include isolation regions and doped regions.

As shown in FIG. 5, first semiconductor structure 502 of semiconductordevice 500 can further include a pad-out interconnect layer 548 abovesemiconductor layer 546. Pad-out interconnect layer 548 can includeinterconnects, e.g., contact pads 550, in one or more ILD layers. Insome embodiments, interconnects in pad-out interconnect layer 548 cantransfer electrical signals between semiconductor device 500 and outsidecircuits, e.g., for pad-out purposes. In some embodiments, firstsemiconductor structure 502 further includes one or more contacts 552extending through semiconductor layer 546 to electrically connectpad-out interconnect layer 548 and interconnect layers 536 and 514. As aresult, processor 540 and array of SRAM cells 510 (and other logiccircuits 542 if any) can be electrically connected to outside circuitsthrough contacts 552 and pad-out interconnect layer 548.

Moreover, processor 540 (and other logic circuits 542 if any) can alsobe electrically connected to array of SRAM cells 510 throughinterconnect layers 536 and 514 as well as bonding contacts 534 and 518.By vertically integrating processor 540 and array of SRAM cells 510, theinterconnect distance can be significantly reduced compared withlaterally arranging processor 540 and array of SRAM cells 510 in thesame plane of a microprocessor chip, which has a chip size in thecentimeter-level. The vertical distance between processor 540 and arrayof SRAM cells 510 is less than 1 mm, according to some embodiments. Inone example, the vertical distance between processor 540 and array ofSRAM cells 510 is between 1 μm and 1 mm (e.g., 1 μm, 2 μm, 3 μm, 4 μm, 5μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70μm, 80 μm, 90 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400μm, 450 μm, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850μm, 900 μm, 950 μm, 1 mm, any range bounded by the lower end by any ofthese values, or in any range defined by any two of these values).

FIGS. 6A and 6B illustrate a fabrication process for forming anexemplary semiconductor structure having a processor and other logiccircuits, according to some embodiments. FIGS. 7A and 7B illustrate afabrication process for forming an exemplary semiconductor structurehaving SRAM, according to some embodiments. FIGS. 8A and 8B illustrate afabrication process for forming an exemplary semiconductor device,according to some embodiments. FIGS. 9A-9C illustrate a fabricationprocess for bonding and dicing an exemplary semiconductor structure,according to some embodiments. FIGS. 10A-10C illustrate a fabricationprocess for dicing and bonding an exemplary semiconductor structure,according to some embodiments. FIG. 11 is a flowchart of an exemplarymethod 1100 for forming a semiconductor device, according to someembodiments. FIG. 12 is a flowchart of another exemplary method 1200 forforming a semiconductor device, according to some embodiments. Examplesof the semiconductor device depicted in FIGS. 6A, 6B, 7A, 7B, 8A, 8B,9A-9C, 10A-10C, 11, and 12 include semiconductor devices 400 and 500depicted in FIGS. 4 and 5, respectively. FIGS. 6A, 6B, 7A, 7B, 8A, 8B,9A-9C, 10A-10C, 11, and 12 will be described together. It is understoodthat the operations shown in methods 1100 and 1200 are not exhaustiveand that other operations can be performed as well before, after, orbetween any of the illustrated operations. Further, some of theoperations may be performed simultaneously, or in a different order thanshown in FIGS. 11 and 12.

As depicted in FIGS. 6A and 6B, a first semiconductor structureincluding a processor, other logic circuits, and a first bonding layerincluding a plurality of first bonding contacts is formed. As depictedin FIGS. 7A and 7B, a second semiconductor structure including an arrayof SRAM cells and a second bonding layer including a plurality of secondbonding contacts is formed. As depicted in FIGS. 8A and 8B, the firstsemiconductor structure and the second semiconductor structure arebonded in a face-to-face manner, such that the first bonding contactsare in contact with the second bonding contacts at a bonding interface.

Referring to FIG. 11, method 1100 starts at operation 1102, in which aplurality of first semiconductor structures are formed on a first wafer.At least one of the first semiconductor structures includes a processorand a first bonding layer including a plurality of first bondingcontacts. The first wafer can be a silicon wafer. In some embodiments,to form the plurality of first semiconductor structures, the processoris formed on the first wafer. In some embodiments, to form theprocessor, a plurality of transistors are formed on the first wafer. Insome embodiments, to form the plurality of first semiconductorstructures, a peripheral circuit of the array of SRAM cells is alsoformed on the first wafer. In some embodiments, to form the plurality offirst semiconductor structures, an interface circuit is also formed onthe first wafer.

As illustrated in FIG. 9A, a plurality of first semiconductor structures906 are formed on a first wafer 902. First wafer 902 can include aplurality of shots separated by scribing lines. Each shot of first wafer902 includes one or more first semiconductor structures 906, accordingto some embodiments. FIGS. 6A and 6B illustrate one example of theformation of first semiconductor structure 906.

As illustrated in FIG. 6A, a plurality of transistors 604 are formed ona silicon substrate 602 (as part of first wafer 902, e.g., a siliconwafer). Transistors 604 can be formed by a plurality of processesincluding, but not limited to, photolithography, dry/wet etch, thin filmdeposition, thermal growth, implantation, chemical mechanical polishing(CMP), and any other suitable processes. In some embodiments, dopedregions are formed in silicon substrate 602 by ion implantation and/orthermal diffusion, which function, for example, as source regions and/ordrain regions of transistors 604. In some embodiments, isolation regions(e.g., STIs) are also formed in silicon substrate 602 by wet/dry etchand thin film deposition. Transistors 604 can form a device layer 606 onsilicon substrate 602. In some embodiments, device layer 606 includes aprocessor 608 and other logic circuits 610. Logic circuits 610 caninclude a peripheral circuit of SRAM and an interface circuit, such as abus circuit or an I/O circuit.

Method 1100 proceeds to operation 1104, as illustrated in FIG. 11, inwhich a first interconnect layer is formed above the processor. Thefirst interconnect layer can include a first plurality of interconnectsin one or more ILD layers. As illustrated in FIG. 6B, an interconnectlayer 614 can be formed above device layer 606 including processor 608and other logic circuits 610. Interconnect layer 614 can includeinterconnects of MEOL and/or BEOL in a plurality of ILD layers to makeelectrical connections with device layer 606. In some embodiments,interconnect layer 614 includes multiple ILD layers and interconnectstherein formed in multiple processes. For example, the interconnects ininterconnect layers 614 can include conductive materials deposited byone or more thin film deposition processes including, but not limitedto, chemical vapor deposition (CVD), physical vapor deposition (PVD),atomic layer deposition (ALD), electroplating, electroless plating, orany combination thereof. Fabrication processes to form interconnects canalso include photolithography, CMP, wet/dry etch, or any other suitableprocesses. The ILD layers can include dielectric materials deposited byone or more thin film deposition processes including, but not limitedto, CVD, PVD, ALD, or any combination thereof. The ILD layers andinterconnects illustrated in FIG. 6B can be collectively referred to asinterconnect layer 614.

Method 1100 proceeds to operation 1106, as illustrated in FIG. 11, inwhich a first bonding layer is formed above the first interconnectlayer. The first bonding layer can include a plurality of first bondingcontacts. As illustrated in FIG. 6B, a bonding layer 616 is formed aboveinterconnect layer 614. Bonding layer 616 can include a plurality ofbonding contacts 618 surrounded by dielectrics. In some embodiments, adielectric layer is deposited on the top surface of interconnect layer614 by one or more thin film deposition processes including, but notlimited to, CVD, PVD, ALD, or any combination thereof. Bonding contacts618 then can be formed through the dielectric layer and in contact withthe interconnects in interconnect layer 614 by first patterning contactholes through the dielectric layer using patterning process (e.g.,photolithography and dry/wet etch of dielectric materials in thedielectric layer). The contact holes can be filled with a conductor(e.g., copper). In some embodiments, filling the contact holes includesdepositing a barrier layer, an adhesion layer, and/or a seed layerbefore depositing the conductor.

Method 1100 proceeds to operation 1108, as illustrated in FIG. 11, inwhich a plurality of second semiconductor structures are formed on asecond wafer. At least one of the second semiconductor structuresincludes an array of SRAM cells and a second bonding layer including aplurality of second bonding contacts. The second wafer can be a siliconwafer. In some embodiments, to form the plurality of secondsemiconductor structures, the array of SRAM cells are formed on thesecond wafer. In some embodiments, to form the array of SRAM cells, aplurality of transistors are formed on the second wafer.

As illustrated in FIG. 9A, a plurality of second semiconductorstructures 908 are formed on a second wafer 904. Second wafer 904 caninclude a plurality of shots separated by scribing lines. Each shot ofsecond wafer 904 includes one or more second semiconductor structures908, according to some embodiments. FIGS. 7A and 7B illustrate oneexample of the formation of second semiconductor structure 908.

As illustrated in FIG. 7A, a plurality of transistors 704 are formed ona silicon substrate 702 (as part of second wafer 904, e.g., a siliconwafer). Transistors 704 can be formed by a plurality of processesincluding, but not limited to, photolithography, dry/wet etch, thin filmdeposition, thermal growth, implantation, CMP, and any other suitableprocesses. In some embodiments, doped regions are formed in siliconsubstrate 702 by ion implantation and/or thermal diffusion, whichfunction, for example, as source regions and/or drain regions oftransistors 704. In some embodiments, isolation regions (e.g., STIs) arealso formed in silicon substrate 702 by wet/dry etch and thin filmdeposition. An array of SRAM cells 710 (each having a plurality oftransistors 704) are thereby formed.

Method 1100 proceeds to operation 1110, as illustrated in FIG. 11, inwhich a second interconnect layer is formed above the array of SRAMcells. The second interconnect layer can include a second plurality ofinterconnects in one or more ILD layers. As illustrated in FIG. 7B, aninterconnect layer 714 can be formed above array of SRAM cells 710.Interconnect layer 714 can include interconnects of MEOL and/or BEOL ina plurality of ILD layers to make electrical connections with array ofSRAM cells 710. In some embodiments, interconnect layer 714 includesmultiple ILD layers and interconnects therein formed in multipleprocesses. For example, the interconnects in interconnect layers 714 caninclude conductive materials deposited by one or more thin filmdeposition processes including, but not limited to, CVD, PVD, ALD,electroplating, electroless plating, or any combination thereof.Fabrication processes to form the interconnects can also includephotolithography, CMP, wet/dry etch, or any other suitable processes.The ILD layers can include dielectric materials deposited by one or morethin film deposition processes including, but not limited to, CVD, PVD,ALD, or any combination thereof. The ILD layers and interconnectsillustrated in FIG. 7B can be collectively referred to as interconnectlayer 714.

Method 1100 proceeds to operation 1112, as illustrated in FIG. 11, inwhich a second bonding layer is formed above the second interconnectlayer. The second bonding layer can include a plurality of secondbonding contacts. As illustrated in FIG. 7B, a bonding layer 716 isformed above interconnect layer 714. Bonding layer 716 can include aplurality of bonding contacts 718 surrounded by dielectrics. In someembodiments, a dielectric layer is deposited on the top surface ofinterconnect layer 714 by one or more thin film deposition processesincluding, but not limited to, CVD, PVD, ALD, or any combinationthereof. Bonding contacts 718 then can be formed through the dielectriclayer and in contact with the interconnects in interconnect layer 714 byfirst patterning contact holes through the dielectric layer usingpatterning process (e.g., photolithography and dry/wet etch ofdielectric materials in the dielectric layer). The contact holes can befilled with a conductor (e.g., copper). In some embodiments, filling thecontact holes includes depositing an adhesion (glue) layer, a barrierlayer, and/or a seed layer before depositing the conductor.

Method 1100 proceeds to operation 1114, as illustrated in FIG. 11, inwhich the first wafer and the second wafer are bonded in a face-to-facemanner, such that the at least one of the first semiconductor structuresis bonded to the at least one of the second semiconductor structures.The first bonding contacts of the first semiconductor structure are incontact with the second bonding contacts of the second semiconductorstructure at a bonding interface. The bonding can be hybrid bonding. Insome embodiments, the second semiconductor structure is above the firstsemiconductor structure after the bonding. In some embodiments, thefirst semiconductor structure is above the second semiconductorstructure after the bonding.

As illustrated in FIG. 9B, first wafer 902 and second wafer 904 arebonded in a face-to-face manner, such that at least one of firstsemiconductor structures 906 is bonded to at least one of secondsemiconductor structures 908 at a bonding interface 909. Although firstwafer 902 is above second wafer 904 after the bonding as shown in FIG.9B, it is understood that second wafer 904 may be above first wafer 902after the bonding in some embodiments. FIG. 8A illustrates one exampleof the formation of bonded first and second semiconductor structures 906and 908.

As illustrated in FIG. 8A, silicon substrate 702 and components formedthereon (e.g., array of SRAM cells 710) are flipped upside down. Bondinglayer 716 facing down is bonded with bonding layer 616 facing up, i.e.,in a face-to-face manner, thereby forming a bonding interface 802 (asshown in FIG. 8B). In some embodiments, a treatment process, e.g., aplasma treatment, a wet treatment, and/or a thermal treatment, isapplied to the bonding surfaces prior to the bonding. Although not shownin FIG. 8A, silicon substrate 602 and components formed thereon (e.g.,device layer 606 including processor 608 and other logic circuits 610)can be flipped upside down, and bonding layer 616 facing down can bebonded with bonding layer 716 facing up, i.e., in a face-to-face manner,thereby forming bonding interface 802. After the bonding, bondingcontacts 718 in bonding layer 716 and bonding contacts 618 in bondinglayer 616 are aligned and in contact with one another, such that arrayof SRAM cells 710 can be electrically connected to device layer 606(e.g., processor 608 and other logic circuits 610). It is understoodthat in the bonded chip, device layer 606 (e.g., processor 608 and otherlogic circuits 610) may be either above or below array of SRAM cells710. Nevertheless, bonding interface 802 can be formed between devicelayer 606 (e.g., processor 608 and other logic circuits 610) and arrayof SRAM cells 710 after the bonding as illustrated in FIG. 8B.

Method 1100 proceeds to operation 1116, as illustrated in FIG. 11, inwhich the first wafer or the second wafer is thinned to form asemiconductor layer. In some embodiments, the first wafer of the firstsemiconductor structure, which is above the second wafer of the secondsemiconductor structure after the bonding, is thinned to form thesemiconductor layer. In some embodiments, the second wafer of the secondsemiconductor structure, which is above the first wafer of the firstsemiconductor structure after the bonding, is thinned to form thesemiconductor layer.

As illustrated in FIG. 8B, the substrate at the top of the bonded chip(e.g., silicon substrate 702 as shown in FIG. 8A) is thinned, so thatthe thinned top substrate can serve as a semiconductor layer 804, forexample, a single-crystal silicon layer. The thickness of the thinnedsubstrate can be between about 200 nm and about 5 μm, such as between200 nm and 5 μm, or between about 150 nm and about 50 μm, such asbetween 150 nm and 50 μm. Silicon substrate 702 can be thinned byprocesses including, but not limited to, wafer grinding, dry etch, wetetch, CMP, any other suitable processes, or any combination thereof. Itis understood that when silicon substrate 602 is the substrate at thetop of the bonded chip, another semiconductor layer may be formed bythinning silicon substrate 602.

Method 1100 proceeds to operation 1118, as illustrated in FIG. 11, inwhich a pad-out interconnect layer is formed above the semiconductorlayer. As illustrated in FIG. 8B, a pad-out interconnect layer 806 isformed above semiconductor layer 804 (the thinned top substrate).Pad-out interconnect layer 806 can include interconnects, such as padcontacts 808, formed in one or more ILD layers. Pad contacts 808 caninclude conductive materials including, but not limited to, W, Co, Cu,Al, doped silicon, silicides, or any combination thereof. The ILD layerscan include dielectric materials including, but not limited to, siliconoxide, silicon nitride, silicon oxynitride, low-k dielectrics, or anycombination thereof. In some embodiments, after the bonding andthinning, contacts 810 are formed extending vertically throughsemiconductor layer 804, for example by wet/dry etch followed bydepositing conductive materials. Contacts 810 can be in contact with theinterconnects in pad-out interconnect layer 806.

Method 1100 proceeds to operation 1120, as illustrated in FIG. 11, inwhich the bonded first and second wafers are diced into a plurality ofdies. At least one of the dies includes the bonded first and secondsemiconductor structures. As illustrated in FIG. 9C, bonded first andsecond wafers 902 and 904 (as shown in FIG. 9B) are diced into aplurality of dies 912. At least one of dies 912 includes bonded firstand second semiconductor structures 906 and 908. In some embodiments,each shot of bonded first and second wafers 902 and 904 is cut frombonded first and second wafers 902 and 904 along the scribing linesusing wafer laser dicing and/or mechanical dicing techniques, therebybecoming respective die 912. Die 912 can include bonded first and secondsemiconductor structures 906 and 908, for example, the bonded structureas shown in FIG. 8B.

Instead of packaging scheme based on wafer-level bonding before dicingas described above with respect to FIGS. 9A-9C and 11, FIGS. 10A-10C and12 illustrate another packaging scheme based on die-level bonding afterdicing, according to some embodiments. Operations 1102, 1104, and 1106of method 1200 in FIG. 12 are described above with respect to method1100 in FIG. 11 and thus, are not repeated. As illustrated in FIG. 10A,a plurality of first semiconductor structures 1006 are formed on a firstwafer 1002. First wafer 1002 can include a plurality of shots separatedby scribing lines. Each shot of first wafer 1002 includes one or morefirst semiconductor structures 1006, according to some embodiments.FIGS. 6A and 6B illustrate one example of the formation of firstsemiconductor structure 1006.

Method 1200 proceeds to operation 1202, as illustrated in FIG. 12, inwhich the first wafer is diced into a plurality of first dies, such thatat least one of the first dies includes the at least one of the firstsemiconductor structures. As illustrated in FIG. 10B, first wafer 1002(as shown in FIG. 10A) is diced into a plurality of dies 1010, such thatat least one die 1010 includes first semiconductor structure 1006. Insome embodiments, each shot of first wafer 1002 is cut from first wafer1002 along the scribing lines using wafer laser dicing and/or mechanicaldicing techniques, thereby becoming respective die 1010. Die 1010 caninclude first semiconductor structure 1006, for example, the structureas shown in FIG. 6B.

Operations 1108, 1110, and 1112 of method 1200 in FIG. 12 are describedabove with respect to method 1100 in FIG. 11 and thus, are not repeated.As illustrated in FIG. 10A, a plurality of second semiconductorstructures 1008 are formed on a second wafer 1004. Second wafer 1004 caninclude a plurality of shots separated by scribing lines. Each shot ofsecond wafer 1004 includes one or more second semiconductor structures1008, according to some embodiments. FIGS. 7A and 7B illustrate oneexample of the formation of second semiconductor structure 1008.

Method 1200 proceeds to operation 1204, as illustrated in FIG. 12, inwhich the second wafer is diced into a plurality of second dies, suchthat at least one of the second dies includes the at least one of thesecond semiconductor structures. As illustrated in FIG. 10B, secondwafer 1004 (as shown in FIG. 10A) is diced into a plurality of dies1012, such that at least one die 1012 includes second semiconductorstructure 1008. In some embodiments, each shot of second wafer 1004 iscut from second wafer 1004 along the scribing lines using wafer laserdicing and/or mechanical dicing techniques, thereby becoming respectivedie 1012. Die 1012 can include second semiconductor structure 1008, forexample, the structure as shown in FIG. 7B.

Method 1200 proceeds to operation 1206, as illustrated in FIG. 12, inwhich the first die and the second die are bonded in a face-to-facemanner, such that the first semiconductor structure is bonded to thesecond semiconductor structure. The first bonding contacts of the firstsemiconductor structure are in contact with the second bonding contactsof the second semiconductor structure at a bonding interface. Asillustrated in FIG. 10C, die 1010 including first semiconductorstructure 1006 and die 1012 including second semiconductor structure1008 are bonded in a face-to-face manner, such that first semiconductorstructure 1006 is bonded to second semiconductor structure 1008 at abonding interface 1014. Although first semiconductor structure 1006 isabove second semiconductor structure 1008 after the bonding as shown inFIG. 10C, it is understood that second semiconductor structure 1008 maybe above first semiconductor structure 1006 after the bonding in someembodiments. FIG. 8A illustrates one example of the formation of bondedfirst and second semiconductor structures 1006 and 1008.

Method 1200 proceeds to operation 1208, as illustrated in FIG. 12, inwhich the first wafer or the second wafer is thinned to form asemiconductor layer. In some embodiments, the first wafer of the firstsemiconductor structure, which is above the second wafer of the secondsemiconductor structure after the bonding, is thinned to form thesemiconductor layer. In some embodiments, the second wafer of the secondsemiconductor structure, which is above the first wafer of the firstsemiconductor structure after the bonding, is thinned to form thesemiconductor layer.

As illustrated in FIG. 8B, the substrate at the top of the bonded chip(e.g., silicon substrate 702 as shown in FIG. 8A) is thinned, so thatthe thinned top substrate can serve as semiconductor layer 804, forexample, a single-crystal silicon layer. Silicon substrate 702 can bethinned by processes including, but not limited to, wafer grinding, dryetch, wet etch, CMP, any other suitable processes, or any combinationthereof. In one example, the thickness of the thinned substrate may bebetween about 1 μm and about 20 μm, such as between 1 μm and 20 μm(e.g., 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 15μm, 20 μm, any range bounded by the lower end by any of these values, orin any range defined by any two of these values), for example, using acombination of etch and CMP processes. It is understood that in someembodiments, by further applying an additional etch process, thethickness of the thinned substrate may be further reduced to below 1 μm,e.g., in the sub-micron range. It is understood that when siliconsubstrate 602 is the substrate at the top of the bonded chip, anothersemiconductor layer may be formed by thinning silicon substrate 602.

Method 1200 proceeds to operation 1210, as illustrated in FIG. 12, inwhich a pad-out interconnect layer is formed above the semiconductorlayer. As illustrated in FIG. 8B, pad-out interconnect layer 806 isformed above semiconductor layer 804 (the thinned top substrate).Pad-out interconnect layer 806 can include interconnects, such as padcontacts 808, formed in one or more ILD layers. Pad contacts 808 caninclude conductive materials including, but not limited to, W, Co, Cu,Al, doped silicon, silicides, or any combination thereof. The ILD layerscan include dielectric materials including, but not limited to, siliconoxide, silicon nitride, silicon oxynitride, low-k dielectrics, or anycombination thereof. In some embodiments, after the bonding andthinning, contacts 810 are formed extending vertically throughsemiconductor layer 804, for example, by wet/dry etch followed bydepositing conductive materials. Contacts 810 can be in contact with theinterconnects in pad-out interconnect layer 806.

According to one aspect of the present disclosure, a semiconductordevice includes a first semiconductor structure including a processorand a first bonding layer including a plurality of first bondingcontacts. The semiconductor device also includes a second semiconductorstructure including an array of SRAM cells and a second bonding layerincluding a plurality of second bonding contacts. The semiconductordevice further includes a bonding interface between the first bondinglayer and the second bonding layer. The first bonding contacts are incontact with the second bonding contacts at the bonding interface.

In some embodiments, the first semiconductor structure does not includean SRAM cell, and the second semiconductor structure does not include aprocessor.

In some embodiments, the first semiconductor structure includes asubstrate, the processor on the substrate, and the first bonding layerabove the processor and the array of SRAM cells.

In some embodiments, the second semiconductor structure includes thesecond bonding layer above the first bonding layer, the array of SRAMcells above the second bonding layer, and a semiconductor layer aboveand in contact with the array of SRAM cells.

In some embodiments, the semiconductor device further includes a pad-outinterconnect layer above the semiconductor layer. In some embodiments,the semiconductor layer includes single-crystal silicon.

In some embodiments, the second semiconductor structure includes asubstrate, the array of SRAM cells on the substrate, and the secondbonding layer above the array of SRAM cells.

In some embodiments, the first semiconductor structure includes thefirst bonding layer above the second bonding layer, the processor abovethe first bonding layer, and a semiconductor layer above and in contactwith the processor.

In some embodiments, the semiconductor device further includes a pad-outinterconnect layer above the semiconductor layer. In some embodiments,the semiconductor layer includes single-crystal silicon.

In some embodiments, the first semiconductor structure further includesa peripheral circuit of the array of SRAM cells. In some embodiments,the first semiconductor structure further includes an interface circuit.In some embodiments, the processor includes a plurality of cores.

In some embodiments, the first semiconductor structure includes a firstinterconnect layer vertically between the first bonding layer and theprocessor, and the second semiconductor structure includes a secondinterconnect layer vertically between the second bonding layer and thearray of SRAM cells.

In some embodiments, the processor is electrically connected to thearray of SRAM cells through the first and second interconnect layers andthe first and second bonding contacts.

In some embodiments, a vertical distance between the processor and thearray of SRAM cells is less than 1 mm.

According to another aspect of the present disclosure, a method forforming a semiconductor device is disclosed. A plurality of firstsemiconductor structures are formed on a first wafer. At least one ofthe first semiconductor structures includes a processor and a firstbonding layer including a plurality of first bonding contacts. Aplurality of second semiconductor structures are formed on a secondwafer. At least one of the second semiconductor structures includes anarray of SRAM cells and a second bonding layer including a plurality ofsecond bonding contacts. The first wafer and the second wafer in arebonded in a face-to-face manner, such that the at least one of the firstsemiconductor structures is bonded to the at least one of the secondsemiconductor structures. The first bonding contacts of the firstsemiconductor structure are in contact with the second bonding contactsof the second semiconductor structure at a bonding interface. The bondedfirst and second wafers are diced into a plurality of dies. At least oneof the dies includes the bonded first and second semiconductorstructures.

In some embodiments, to form the plurality of first semiconductorstructures, the processor is formed on the first wafer, a firstinterconnect layer is formed above the processor, and the first bondinglayer is formed above the first interconnect layer. In some embodiments,to form the processor, a plurality of transistors are formed on thefirst wafer.

In some embodiments, to form the plurality of first semiconductorstructures, a peripheral circuit of the array of SRAM cells is formed onthe first wafer. In some embodiments, to form the plurality of firstsemiconductor structures, an interface circuit is formed on the firstwafer.

In some embodiments, to form the plurality of second semiconductorstructures, the array of SRAM cells are formed on the second wafer, asecond interconnect layer is formed above the array of SRAM cells, andthe second bonding layer is formed above the second interconnect layer.

In some embodiments, to form the array of SRAM cells, a plurality oftransistors are formed on the second wafer.

In some embodiments, the second semiconductor structure is above thefirst semiconductor structure after the bonding. In some embodiments,after the bonding and prior to the dicing, the second wafer is thinnedto form a semiconductor layer, and a pad-out interconnect layer isformed above the semiconductor layer.

In some embodiments, the first semiconductor structure is above thesecond semiconductor structure after the bonding. In some embodiments,after the bonding and prior to the dicing, the first wafer is thinned toform a semiconductor layer, and a pad-out interconnect layer is formedabove the semiconductor layer.

In some embodiments, the bonding includes hybrid bonding.

According to still another aspect of the present disclosure, a methodfor forming a semiconductor device is disclosed. A plurality of firstsemiconductor structures are formed on a first wafer. At least one ofthe first semiconductor structures includes a processor and a firstbonding layer including a plurality of first bonding contacts. The firstwafer is diced into a plurality of first dies, such that at least one ofthe first dies includes the at least one of the first semiconductorstructures. A plurality of second semiconductor structures are formed ona second wafer. At least one of the second semiconductor structuresincludes an array of SRAM cells and a second bonding layer including aplurality of second bonding contacts. The second wafer is diced into aplurality of second dies, such that at least one of the second diesincludes the at least one of the second semiconductor structures. Thefirst die and the second die are bonded in a face-to-face manner, suchthat the first semiconductor structure is bonded to the secondsemiconductor structure. The first bonding contacts of the firstsemiconductor structure are in contact with the second bonding contactsof the second semiconductor structure at a bonding interface.

In some embodiments, to form the plurality of first semiconductorstructures, the processor is formed on the first wafer, a firstinterconnect layer is formed above the processor, and the first bondinglayer is formed above the first interconnect layer. In some embodiments,to form the processor, a plurality of transistors are formed on thefirst wafer.

In some embodiments, to form the plurality of first semiconductorstructures, a peripheral circuit of the array of SRAM cells is formed onthe first wafer. In some embodiments, to form the plurality of firstsemiconductor structures, an interface circuit is formed on the firstwafer.

In some embodiments, to form the plurality of second semiconductorstructures, the array of SRAM cells are formed on the second wafer, asecond interconnect layer is formed above the array of SRAM cells, andthe second bonding layer is formed above the second interconnect layer.

In some embodiments, to form the array of SRAM cells, a plurality oftransistors are formed on the second wafer.

In some embodiments, the second semiconductor structure is above thefirst semiconductor structure after the bonding. In some embodiments,the second wafer is thinned to form a semiconductor layer after thebonding, and a pad-out interconnect layer is formed above thesemiconductor layer.

In some embodiments, the first semiconductor structure is above thesecond semiconductor structure after the bonding. In some embodiments,the first wafer is thinned to form a semiconductor layer after thebonding, and a pad-out interconnect layer is formed above thesemiconductor layer.

In some embodiments, the bonding includes hybrid bonding.

The foregoing description of the specific embodiments will so reveal thegeneral nature of the present disclosure that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

Embodiments of the present disclosure have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The Summary and Abstract sections may set forth one or more but not allexemplary embodiments of the present disclosure as contemplated by theinventor(s), and thus, are not intended to limit the present disclosureand the appended claims in any way.

The breadth and scope of the present disclosure should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A semiconductor device, comprising: a firstsemiconductor structure comprising a processor and a first bonding layercomprising a plurality of first bonding contacts; a second semiconductorstructure comprising an array of static random-access memory (SRAM)cells and a second bonding layer comprising a plurality of secondbonding contacts; and a bonding interface between the first bondinglayer and the second bonding layer, wherein the first bonding contactsare in contact with the second bonding contacts at the bondinginterface.
 2. The semiconductor device of claim 1, wherein the firstsemiconductor structure does not comprise an SRAM cell, and the secondsemiconductor structure does not comprise a processor.
 3. Thesemiconductor device of claim 1, wherein the first semiconductorstructure comprises: a substrate; the processor on the substrate; andthe first bonding layer above the processor.
 4. The semiconductor deviceof claim 3, wherein the second semiconductor structure comprises: thesecond bonding layer above the first bonding layer; the array of SRAMcells above the second bonding layer; and a semiconductor layer aboveand in contact with the array of SRAM cells.
 5. The semiconductor deviceof claim 4, further comprising a pad-out interconnect layer above thesemiconductor layer, wherein the semiconductor layer comprisessingle-crystal silicon.
 6. The semiconductor device of claim 1, whereinthe second semiconductor structure comprises: a substrate; the array ofSRAM cells on the substrate; and the second bonding layer above thearray of SRAM cells.
 7. The semiconductor device of claim 6, wherein thefirst semiconductor structure comprises: the first bonding layer abovethe second bonding layer; the processor above the first bonding layer;and a semiconductor layer above and in contact with the processor. 8.The semiconductor device of claim 7, further comprising a pad-outinterconnect layer above the semiconductor layer, wherein thesemiconductor layer comprises single-crystal silicon.
 9. Thesemiconductor device of claim 1, wherein the first semiconductorstructure further comprises at least a peripheral circuit of the arrayof SRAM cells or an interface circuit.
 10. The semiconductor device ofclaim 1, wherein the first semiconductor structure comprises a firstinterconnect layer vertically between the first bonding layer and theprocessor, and the second semiconductor structure comprises a secondinterconnect layer vertically between the second bonding layer and thearray of SRAM cells.
 11. The semiconductor device of claim 10, whereinthe processor is electrically connected to the array of SRAM cellsthrough the first and second interconnect layers and the first andsecond bonding contacts.
 12. A method for forming a semiconductordevice, comprising: forming a plurality of first semiconductorstructures on a first wafer, wherein at least one of the firstsemiconductor structures comprises a processor and a first bonding layercomprising a plurality of first bonding contacts; forming a plurality ofsecond semiconductor structures on a second wafer, wherein at least oneof the second semiconductor structures comprises an array of staticrandom-access memory (SRAM) cells and a second bonding layer comprisinga plurality of second bonding contacts; bonding the first wafer and thesecond wafer in a face-to-face manner, such that the at least one of thefirst semiconductor structures is bonded to the at least one of thesecond semiconductor structures, wherein the first bonding contacts ofthe first semiconductor structure are in contact with the second bondingcontacts of the second semiconductor structure at a bonding interface;and dicing the bonded first and second wafers into a plurality of dies,wherein at least one of the dies comprises the bonded first and secondsemiconductor structures.
 13. The method of claim 12, wherein formingthe plurality of first semiconductor structures comprises: forming theprocessor on the first wafer; forming a first interconnect layer abovethe processor; and forming the first bonding layer above the firstinterconnect layer.
 14. The method of claim 13, wherein forming theplurality of first semiconductor structures further comprises forming atleast one or a peripheral circuit of the array of SRAM cells or aninterface circuit on the first wafer.
 15. The method of claim 12,wherein forming the plurality of second semiconductor structurescomprises: forming the array of SRAM cells on the second wafer; forminga second interconnect layer above the array of SRAM cells; and formingthe second bonding layer above the second interconnect layer.
 16. Themethod of claim 12, wherein the second semiconductor structure is abovethe first semiconductor structure after the bonding; and the methodfurther comprises, after the bonding and prior to the dicing: thinningthe second wafer to form a semiconductor layer; and forming a pad-outinterconnect layer above the semiconductor layer.
 17. The method ofclaim 12, wherein the first semiconductor structure is above the secondsemiconductor structure after the bonding; and the method furthercomprises, after the bonding and prior to the dicing: thinning the firstwafer to form a semiconductor layer; and forming a pad-out interconnectlayer above the semiconductor layer.
 18. A method for forming asemiconductor device, comprising: forming a plurality of firstsemiconductor structures on a first wafer, wherein at least one of thefirst semiconductor structures comprises a processor and a first bondinglayer comprising a plurality of first bonding contacts; dicing the firstwafer into a plurality of first dies, such that at least one of thefirst dies comprises the at least one of the first semiconductorstructures; forming a plurality of second semiconductor structures on asecond wafer, wherein at least one of the second semiconductorstructures comprises an array of static random-access memory (SRAM)cells and a second bonding layer comprising a plurality of secondbonding contacts; dicing the second wafer into a plurality of seconddies, such that at least one of the second dies comprises the at leastone of the second semiconductor structures; and bonding the first dieand the second die in a face-to-face manner, such that the firstsemiconductor structure is bonded to the second semiconductor structure,wherein the first bonding contacts of the first semiconductor structureare in contact with the second bonding contacts of the secondsemiconductor structure at a bonding interface.
 19. The method of claim18, wherein forming the plurality of first semiconductor structurescomprises: forming the processor on the first wafer; forming a firstinterconnect layer above the processor; and forming the first bondinglayer above the first interconnect layer.
 20. The method of claim 18,wherein forming the plurality of second semiconductor structurescomprises: forming the array of SRAM cells on the second wafer; forminga second interconnect layer above the array of SRAM cells; and formingthe second bonding layer above the second interconnect layer.